Predicting temporary threshold shifts in a bottlenose dolphin (Tursiops truncatus) : the effects of noise level and duration

Author Posting. © Acoustical Society of America, 2009. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 125 (2009): 1816-1826, doi:10.1121/1.3068456.Noise levels in the ocean are increasing and are expected to affect marine mammals. To examine the auditory effects of noise on odontocetes, a bottlenose dolphin (Tursiops truncatus) was exposed to octave-band noise (4–8 kHz) of varying durations (<2–30 min) and sound pressures (130–178 dB re 1 µPa). Temporary threshold shift (TTS) occurrence was quantified in an effort to (i) determine the sound exposure levels (SELs) (dB re 1 µPa2 s) that induce TTS and (ii) develop a model to predict TTS onset. Hearing thresholds were measured using auditory evoked potentials. If SEL was kept constant, significant shifts were induced by longer duration exposures but not for shorter exposures. Higher SELs were required to induce shifts in shorter duration exposures. The results did not support an equal-energy model to predict TTS onset. Rather, a logarithmic algorithm, which increased in sound energy as exposure duration decreased, was a better predictor of TTS. Recovery to baseline hearing thresholds was also logarithmic (approximately −1.8 dB/doubling of time) but indicated variability including faster recovery rates after greater shifts and longer recoveries necessary after longer duration exposures. The data reflected the complexity of TTS in mammals that should be taken into account when predicting odontocete TTS.This work was funded by the Office of Naval Research Grant No. 00014-098-1-687 to P.E.N. and the support of Bob Gisiner and Mardi Hasting is noted. Additional support came from SeaSpace to T.A.M

Avaliação Agronômica da Ameixeira 'Letícia' em Vacaria, RS.

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Density-functional study of hydrogen chemisorption on vicinal Si(001) surfaces

Relaxed atomic geometries and chemisorption energies have been calculated for the dissociative adsorption of molecular hydrogen on vicinal Si(001) surfaces. We employ density-functional theory, together with a pseudopotential for Si, and apply the generalized gradient approximation by Perdew and Wang to the exchange-correlation functional. We find the double-atomic-height rebonded D_B step, which is known to be stable on the clean surface, to remain stable on partially hydrogen-covered surfaces. The H atoms preferentially bind to the Si atoms at the rebonded step edge, with a chemisorption energy difference with respect to the terrace sites of >sim 0.1 eV. A surface with rebonded single atomic height S_A and S_B steps gives very similar results. The interaction between H-Si-Si-H mono-hydride units is shown to be unimportant for the calculation of the step-edge hydrogen-occupation. Our results confirm the interpretation and results of the recent H_2 adsorption experiments on vicinal Si surfaces by Raschke and Hoefer described in the preceding paper.Comment: 13 pages, 8 figures, submitted to Phys. Rev. B. Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

In Vivo Time- Resolved Microtomography Reveals the Mechanics of the Blowfly Flight Motor

Dipteran flies are amongst the smallest and most agile of flying animals. Their wings are driven indirectly by large power muscles, which cause cyclical deformations of the thorax that are amplified through the intricate wing hinge. Asymmetric flight manoeuvres are controlled by 13 pairs of steering muscles acting directly on the wing articulations. Collectively the steering muscles account for <3% of total flight muscle mass, raising the question of how they can modulate the vastly greater output of the power muscles during manoeuvres. Here we present the results of a synchrotron-based study performing micrometre-resolution, time-resolved microtomography on the 145 Hz wingbeat of blowflies. These data represent the first four-dimensional visualizations of an organism's internal movements on sub-millisecond and micrometre scales. This technique allows us to visualize and measure the three-dimensional movements of five of the largest steering muscles, and to place these in the context of the deforming thoracic mechanism that the muscles actuate. Our visualizations show that the steering muscles operate through a diverse range of nonlinear mechanisms, revealing several unexpected features that could not have been identified using any other technique. The tendons of some steering muscles buckle on every wingbeat to accommodate high amplitude movements of the wing hinge. Other steering muscles absorb kinetic energy from an oscillating control linkage, which rotates at low wingbeat amplitude but translates at high wingbeat amplitude. Kinetic energy is distributed differently in these two modes of oscillation, which may play a role in asymmetric power management during flight control. Structural flexibility is known to be important to the aerodynamic efficiency of insect wings, and to the function of their indirect power muscles. We show that it is integral also to the operation of the steering muscles, and so to the functional flexibility of the insect flight motor

Passenger car data – a new source of real-time weather information for nowcasting, forecasting, and road safety

Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019

Synthesis of ‘unfeasible’ zeolites

Zeolites are porous aluminosilicate materials that have found applications in many different technologies. However, although simulations suggest that there are millions of possible zeolite topologies, only a little over 200 zeolite frameworks of all compositions are currently known, of which about 50 are pure silica materials. This is known as the zeolite conundrum—why have so few of all the possible structures been made? Several criteria have been formulated to explain why most zeolites are unfeasible synthesis targets. Here we demonstrate the synthesis of two such unfeasible’ zeolites, IPC-9 and IPC-10, through the assembly–disassembly–organization–reassembly mechanism. These new high-silica zeolites have rare characteristics, such as windows that comprise odd-membered rings. Their synthesis opens up the possibility of preparing other zeolites that have not been accessible by traditional solvothermal synthetic methods. We envisage that these findings may lead to a step change in the number and types of zeolites available for future applications

The function of the alula in avian flight

The alula is a small structure located at the joint between the hand-wing and arm-wing of birds and is known to be used in slow flight with high angles of attack such as landing. It is assumed to function similarly to a leading-edge slat that increases lift and delays stall. However, in spite of its universal presence in flying birds and the wide acceptance of stall delay as its main function, how the alula delays the stall and aids the flight of birds remains unclear. Here, we investigated the function of alula on the aerodynamic performance of avian wings based on data from flight tasks and wind-tunnel experiments. With the alula, the birds performed steeper descending flights with greater changes in body orientation. Force measurements revealed that the alula increases the lift and often delays the stall. Digital particle image velocimetry showed that these effects are caused by the streamwise vortex, formed at the tip of the alula, that induces strong downwash and suppresses the flow separation over the wing surface. This is the first experimental evidence that the alula functions as a vortex generator that increases the lift force and enhances manoeuvrability in flights at high angles of attack.open1

Pseudopotential study of binding properties of solids within generalized gradient approximations: The role of core-valence exchange-correlation

In ab initio pseudopotential calculations within density-functional theory the nonlinear exchange-correlation interaction between valence and core electrons is often treated linearly through the pseudopotential. We discuss the accuracy and limitations of this approximation regarding a comparison of the local density approximation (LDA) and generalized gradient approximations (GGA), which we find to describe core-valence exchange-correlation markedly different. (1) Evaluating the binding properties of a number of typical solids we demonstrate that the pseudopotential approach and namely the linearization of core-valence exchange-correlation are both accurate and limited in the same way in GGA as in LDA. (2) Examining the practice to carry out GGA calculations using pseudopotentials derived within LDA we show that the ensuing results differ significantly from those obtained using pseudopotentials derived within GGA. As principal source of these differences we identify the distinct behavior of core-valence exchange-correlation in LDA and GGA which, accordingly, contributes substantially to the GGA induced changes of calculated binding properties.Comment: 13 pages, 6 figures, submitted to Phys. Rev. B, other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm